The extent and nature of symbolic behavior among Neandertals are obscure. Although evidence for Neandertal body ornamentation has been proposed, all cave painting has been attributed to modern humans. Here we present dating results for three sites in Spain that show that cave art emerged in Iberia substantially earlier than previously thought. Uranium-thorium (U-Th) dates on carbonate crusts overlying paintings provide minimum ages for a red linear motif in La Pasiega (Cantabria), a hand stencil in Maltravieso (Extremadura), and red-painted speleothems in Ardales (Andalucía). Collectively, these results show that cave art in Iberia is older than 64.8 thousand years (ka). This cave art is the earliest dated so far and predates, by at least 20 ka, the arrival of modern humans in Europe, which implies Neandertal authorship.

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Rationale Boron isotope analysis of marine carbonates by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) offers the potential for rapid sample throughput, and the means to examine micron‐scale variations in the δ11B signatures of fossil skeletons and shells/tests of marine organisms. Existing studies demonstrate an acceptable level of reproducibility is achievable, but also typically show a level of accuracy outside the limits required by most applications. Here we investigate matrix interference effects as a cause of inaccuracy and imprecision. Methods Analyses were performed on a standard format Thermo Scientific Neptune Plus MC‐ICP mass spectrometer coupled to a New Wave Research 193 nm ArF laser ablation system. The effects of matrix interference on δ11B analysis were investigated through analyses of a set of reference materials with differing B/Ca ratios. Three approaches to correct for matrix‐induced effects were trialled: (1) use of matrix‐matched standards, (2) utilisation of the relationship between δ11B inaccuracy and11B/43Ca, 11B/40ArCa4+ or 11B/Cainterference from three reference materials with known δ11B values and varying B/Ca ratios, and (3) direct characterisation of the (sloping) interference itself. Results Matrix interference from scattered Ca ions on 10B can impede both the accuracy and the reproducibility of δ11B analysis by LA‐MC‐ICP‐MS. Based on analyses of two in‐house reference materials, deep sea coral PS69/3181 and inorganic calcite UWC‐1, we find approach 2, following the 11B/Cainterference relationship, gives the best mean accuracies (within 0.4‰ of solution values) and external reproducibilities (± 0.5‰ 2 SD for PS69/3181). This approach has been applied to analyses of an annual growth cycle of a Siderastrea siderea coral and eight Cibicidoides wuellerstorfi benthic foraminifera. Both coral and foraminifera data match solution MC‐ICP‐MS analyses within reported uncertainties. Conclusions LA‐MC‐ICP‐MS can produce accurate and precise δ11B data to a 0.5‰ (2σ) level on <0.3 ng B after correction for Ca interference effects.

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